In recent years, a variety of projectors have been widely used in various video applications. By the projector, an image signal provided by an image signal source is enlarged and shown on a projection screen. For reducing power consumption and longer life, the illumination system of the current projector employs a solid-state light-emitting element (e.g. light emitting diode or laser diode) to replace the conventional high intensity discharge (HID) lamp.
Generally, the illumination system of the projector should emit three primary colors of light, i.e. red light (R), green light (G) and blue light (B). As for the luminous efficiency of the solid-state light-emitting element, the luminous efficiency of the blue solid-state light-emitting element>the luminous efficiency of the red solid-state light-emitting element>>the luminous efficiency of the green solid-state light-emitting element. Since the green solid-state light-emitting element has poor luminous efficiency, the green light is produced by using a blue solid-state light-emitting element and a plate containing phosphor or wavelength conversion material. That is, the uses of the blue solid-state light-emitting element and the plate may directly emit the green light in replace of the green blue solid-state light-emitting element. Consequently, the luminous efficiency of the whole illumination system is enhanced.
However, since the phosphor or the wavelength conversion material contained in the plate of the conventional illumination system is readily affected by temperature, a thermal quenching problem possibly occurs. Due to the thermal quenching problem, the luminous efficiency of the converted and outputted green light is largely decreased as the temperature is increased.
FIG. 1A schematically illustrates the architecture of a conventional illumination system. FIG. 1B schematically illustrates the configuration of a phosphor wheel used in the conventional illumination system as shown in FIG. 1A. The conventional illumination system 1 comprises a blue LED 11, a red LED 12, a phosphor wheel 13 and a dichroic minor 14. The dichroic minor 14 is located between the blue LED 11 and the phosphor wheel 13. The blue LED 11 is used for emitting blue light. The blue light is transmitted through the dichroic minor 14 and directed to an optical path. The red LED 12 is used for emitting red light. The red light is reflected by the dichroic minor 14 and directed to the optical path. The rotation of the phosphor wheel 13 is driven by a motor (not shown). The phosphor wheel 13 comprises a first section 131, a second section 132 and a third section 133. The first section 131 contains phosphor or wavelength conversion material. By the phosphor or wavelength conversion material, the blue light emitted by the blue LED 11 is excited as green light to be outputted. The second section 132 and the third section 133 fail to contain phosphor or wavelength conversion material and are transparent sections. For example, the second section 132 and the third section 133 are respectively a blue color filter and a red color filter. Consequently, the blue light and the red light are transmissible through the second section 132 and the third section 133, respectively.
In a first time segment, the blue LED 11 is enabled, the red LED 12 is disabled, and the phosphor wheel 13 is driven to rotate by the motor such that the first section 131 is located in the optical path. The blue light emitted by the blue LED 11 is excited as green light by the phosphor or wavelength conversion material, and thus the green light is outputted in the first time segment. Next, in a second time segment, the blue LED 11 is also enabled, the red LED 12 is also disabled, and the phosphor wheel 13 is driven to rotate by the motor such that the second section 132 is located in the optical path. The blue light emitted by the blue LED 11 is transmitted through the second section 132 of the phosphor wheel 13, and thus the blue light is outputted in the second time segment. Next, in a third time segment, the blue LED 11 is disabled, the red LED 12 is enabled, and the phosphor wheel 13 is driven to rotate by the motor such that the third section 133 is located in the optical path. The red light emitted by the red LED 12 is transmitted through the third section 133 of the phosphor wheel 13, and thus the red light is outputted in the third time segment.
However, the conventional illumination system 1 is suffered from a wheel rotational unbalance problem, and different colors of light fail to be mixed at the same time spot. That is, the conventional illumination system 1 can not be operated in the BrightSync mode, and thus the brightness is usually unsatisfied.
FIG. 2A schematically illustrates the architecture of another conventional illumination system. FIG. 2B schematically illustrates the configuration of a phosphor wheel used in the conventional illumination system as shown in FIG. 2A. The conventional illumination system 2 comprises a blue LED 21, a red LED 22, a phosphor wheel 23 and a dichroic minor 24. The phosphor wheel 23 is located between the blue LED 21 and the dichroic mirror 24. The blue LED 21 is used for emitting blue light and directing the blue light to an optical path. In different time sequences, the blue light is transmitted through different time segments of the phosphor wheel 23, so that the blue light is outputted or the blue light is excited as green light to be outputted. The blue light or the green light outputted from the phosphor wheel 23 is then transmitted through the dichroic mirror 24. The red LED 22 is used for emitting red light. The red light is reflected by the dichroic mirror 24 and directed to the optical path. The rotation of the phosphor wheel 23 is driven by a motor (not shown). The phosphor wheel 23 comprises a first section 231 and a second section 232. The first section 231 contains phosphor or wavelength conversion material. By the phosphor or wavelength conversion material, the blue light emitted by the blue LED 21 is excited as green light to be outputted. The second section 232 fails to contain phosphor or wavelength conversion material and is a transparent section. For example, the second section 132 is a blue color filter. Consequently, the blue light is transmissible through the second section 232.
In a first time segment, the blue LED 21 is enabled, the red LED 22 is disabled, and the phosphor wheel 23 is driven to rotate by the motor such that the first section 231 is located in the optical path. The blue light emitted by the blue LED 21 is excited as green light by the phosphor or wavelength conversion material, and thus the green light is outputted in the first time segment. Next, in a second time segment, the blue LED 21 is also enabled, the red LED 22 is also disabled, and the phosphor wheel 23 is driven to rotate by the motor such that the second section 232 is located in the optical path. The blue light emitted by the blue LED 21 is transmitted through the second section 232 of the phosphor wheel 23, and thus the blue light is outputted in the second time segment. Next, in a third time segment, the blue LED 21 is disabled, the red LED 22 is enabled, and the phosphor wheel 23 is disabled. The red light from the red LED 22 is reflected by the dichroic mirror 24 and directed to the optical path.
However, the conventional illumination system 2 is also suffered from the wheel rotational unbalance problem. In addition, it is difficult to design the dichroic mirror 24, and the brightness of the green light is impaired.
FIG. 3A schematically illustrates the architecture of another conventional illumination system. FIG. 3B schematically illustrates the configuration of a phosphor wheel used in the conventional illumination system as shown in FIG. 3A. The conventional illumination system 3 comprises a blue LED 31 and a phosphor wheel 32. The blue LED 31 is used for emitting blue light and directing the blue light to an optical path. The rotation of the phosphor wheel 33 is driven by a motor (not shown). The phosphor wheel 32 comprises a first section 321, a second section 322 and a third section 323. The first section 321 contains first phosphor or first wavelength conversion material. By the first phosphor or first wavelength conversion material, the blue light emitted by the blue LED 31 is excited as green light to be outputted. The second section 322 fails to contain phosphor or wavelength conversion material and is a transparent section. For example, the second section 132 is a blue color filter. Consequently, the blue light is transmissible through the second section 322. The third section 323 contains second phosphor or second wavelength conversion material. By the second phosphor or second wavelength conversion material, the blue light emitted by the blue LED 31 is excited as red light to be outputted.
In a first time segment, the blue LED 31 is enabled, and the phosphor wheel 32 is driven to rotate by the motor such that the first section 321 is located in the optical path. The blue light emitted by the blue LED 31 is excited as green light by the first phosphor or first wavelength conversion material, and thus the green light is outputted in the first time segment. Next, in a second time segment, the blue LED 31 is also enabled, and the phosphor wheel 32 is driven to rotate by the motor such that the second section 322 is located in the optical path. The blue light emitted by the blue LED 31 is transmitted through the second section 322 of the phosphor wheel 32, and thus the blue light is outputted in the second time segment. Next, in a third time segment, the blue LED 31 is also enabled, and the phosphor wheel 32 is driven to rotate by the motor such that the third section 323 is located in the optical path. The blue light emitted by the blue LED 31 is excited as red light by the second phosphor or second wavelength conversion material, and thus the red light is outputted in the first time segment.
Although the conventional illumination system 3 is relatively power-saving, the wheel rotational unbalance problem fails to be effectively solved. Moreover, since different colors of light fail to be mixed at the same time spot, the conventional illumination system 3 can not be operated in the BrightSync mode. Under this circumstance, the brightness is usually unsatisfied.